U.S. patent application number 12/019381 was filed with the patent office on 2009-07-30 for reverse link channel estimation using common and dedicated pilot channels.
Invention is credited to ANGEL LOZANO, Sivarama Venkatesan.
Application Number | 20090191835 12/019381 |
Document ID | / |
Family ID | 40899739 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090191835 |
Kind Code |
A1 |
LOZANO; ANGEL ; et
al. |
July 30, 2009 |
REVERSE LINK CHANNEL ESTIMATION USING COMMON AND DEDICATED PILOT
CHANNELS
Abstract
The present invention provides a method of channel estimation
implemented in a receiver having multiple antennas configured to
receive at least one common pilot available to a plurality of users
and a plurality of dedicated pilots. Each dedicated pilot is
allocated to one of the plurality of users. The method includes
estimating at least one first channel associated with a first user
and at least one second channel associated with a second user based
on observations of the plurality of dedicated pilots and of said at
least one common pilot.
Inventors: |
LOZANO; ANGEL; (Barcelona,
ES) ; Venkatesan; Sivarama; (Milltown, NJ) |
Correspondence
Address: |
MARK W. SINCELL;Williams, Morgan & Amerson, P.C.
Suite 1100, 10333 Richmond
Houston
TX
77042
US
|
Family ID: |
40899739 |
Appl. No.: |
12/019381 |
Filed: |
January 24, 2008 |
Current U.S.
Class: |
455/334 ;
375/340 |
Current CPC
Class: |
H04L 5/005 20130101;
H04L 5/0051 20130101; H04L 25/0226 20130101 |
Class at
Publication: |
455/334 ;
375/340 |
International
Class: |
H03D 1/00 20060101
H03D001/00; H04B 1/16 20060101 H04B001/16; H04L 27/06 20060101
H04L027/06 |
Claims
1. A method of channel estimation implemented in a receiver having
multiple antennas configured to receive at least one common pilot
available to a plurality of users and a plurality of dedicated
pilots, each dedicated pilot being allocated to one of the
plurality of users, comprising: estimating at least one first
channel associated with a first user and at least one second
channel associated with a second user based on observations of the
plurality of dedicated pilots and of said at least one common
pilot.
2. The method of claim 1, wherein estimating said at least one
first channel and said at least one second channel comprises:
estimating said at least one first channel based on observations of
at least one first dedicated pilot allocated to the first user; and
estimating said at least one a second channel based on observations
of at least one second dedicated pilot allocated to the second
user.
3. The method of claim 2, comprising estimating at least one
composite channel associated with the first and second users based
on observations of said at least one common pilot.
4. The method of claim 3, wherein estimating said at least one
first channel and said at least one second channel comprises:
refining said at least one estimated first channel based on said at
least one estimated composite channel; and refining said at least
one estimated second channel based on said at least one estimated
composite channel.
5. The method of claim 1, wherein estimating said at least one
first channel comprises estimating said at least one first channel
based on observations of at least one first dedicated pilot
allocated to the first user and the observations of said at least
one common pilot.
6. The method of claim 5, wherein estimating said at least one
second channel comprises estimating said at least one second
channel based on observations of at least one second dedicated
pilot allocated to the second user and the observations of said at
least one common pilot.
7. The method of claim 1, wherein estimating said at least one
first channel and said at least one second channel comprises
concurrently estimating said at least one first channel and said at
least one second channel based on observations of at least one
first dedicated pilot allocated to the first user, observations of
at least one second dedicated pilot allocated to the second user,
and the observations of said at least one common pilot.
8. The method of claim 7, wherein concurrently estimating said at
least one first channel and said at least one second channel
comprises concurrently estimating said at least one first channel
and said at least one second channel to account for coupling of the
first and second channels indicated in the observations of said at
least one common pilot.
9. A method of channel estimation implemented in a receiver having
multiple receive antennas configured to receive at least one common
pilot available to a plurality of transmit antennas associated with
at least one user and a plurality of dedicated pilots, each
dedicated pilot being allocated to one of the plurality of transmit
antennas, comprising: estimating a plurality of channels associated
with the plurality of transmit antennas based on observations of
the plurality of dedicated pilots and of said at least one common
pilot.
10. The method of claim 9, wherein estimating the plurality of
channels comprises: estimating the plurality of channels based on
observations of the plurality of dedicated pilots; estimating at
least one composite channel associated with the plurality of users
based on observations of said at least one common pilot; and
refining the plurality of estimated channels based on said at least
one estimated composite channel.
11. The method of claim 9, wherein estimating the plurality of
channels comprises independently estimating channels associated
with each antenna based on observations of at least one dedicated
pilot allocated to a corresponding antenna and the observations of
said at least one common pilot.
12. The method of claim 9, wherein estimating the plurality of
channels comprises concurrently estimating the plurality of
channels based on observations of the dedicated pilots allocated to
the plurality of users and the observations of said at least one
common pilot.
13. A method of channel estimation implemented in a plurality of
receivers each having at least one receive antenna configured to
receive at least one common pilot available to a plurality of users
and a plurality of dedicated pilots, each dedicated pilot being
allocated to one of the users, comprising: estimating a plurality
of channels associated with the plurality of users based on
observations of the plurality of dedicated pilots and of said at
least one common pilot.
14. The method of claim 13, wherein estimating the plurality of
channels comprises: estimating the plurality of channels based on
observations of the plurality of dedicated pilots; estimating at
least one composite channel associated with the plurality of users
based on observations of said at least one common pilot; and
refining the plurality of estimated channels based on said at least
one estimated composite channel.
15. The method of claim 13, wherein estimating the plurality of
channels comprises independently estimating channels associated
with each user based on observations of at least one dedicated
pilot allocated to a corresponding user and the observations of
said at least one common pilot.
16. The method of claim 13, wherein estimating the plurality of
channels comprises concurrently estimating the plurality of
channels based on observations of the dedicated pilots allocated to
the plurality of users and the observations of said at least one
common pilot.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to communication systems,
and, more particularly, to wireless communication systems.
[0003] 2. Description of the Related Art
[0004] Conventional wireless communication systems include a
network of base stations, base station routers, and/or other
wireless access points that are used to provide wireless
connectivity to access terminals in geographic areas (or cells)
associated with the network. Information may be communicated
between the network and the access terminals over an air interface
using wireless communication links that typically include multiple
channels. The channels include forward link (or downlink) channels
that carry signals from the base stations to the access terminals
and reverse link (or uplink) channels that carry signals from the
access terminals to the base station. The channels may be defined
using time slots, frequencies, scrambling codes or sequences, or
any combination thereof. For example, the channels in a Code
Division Multiple Access (CDMA) system are defined by modulating
signals transmitted on the channels using orthogonal codes or
sequences. For another example, the channels in an Orthogonal
Frequency Division Multiplexing (OFDM) system are defined using a
set of orthogonal frequencies known as tones or subcarriers.
[0005] Next (4th) generation wireless systems such as 802.16e
WiMAX, UMTS Long Term Evolution (LTE) and cdma2000 EV-DO Revision C
Ultra Mobile Broadband (UMB) are based on Orthogonal Frequency
Division Multiple Access. In OFDMA, the transmitted signal consists
of narrowband tones that are nearly orthogonal to each other in the
frequency domain. A group of tones transmitted over the duration of
one time slot (or frame) constitutes the smallest scheduling
resource unit, also known as a tile, a resource block (RB), or a
base node (BN). Different tones belonging to a tile may be
scattered across the entire carrier frequency band used by the
OFDMA system so that each tile transmission experiences diversified
channels and interference on each sub-carrier. Alternatively, a
tile can be formed of a contiguous set of tones so that the channel
and interference experienced by the tile are more localized. Hybrid
Automatic Repeat reQuest (HARQ) is employed to increase the
capacity of the OFDMA system. To this end, the encoder packet
transmission includes multiple HARQ interlaces repeating every
certain number of frames and having a fixed maximum allowed number
of sub-packet retransmissions.
[0006] Modern wireless systems typically implement coherent
detection in both the forward and reverse links. This requires the
transmission of pilot signals (which may also be referred to as
reference signals or training signals) that can be used as a
reference to estimate the amplitude and phase of the fading channel
that carries the uplink/downlink signals. For example, on the
reverse link, coherent detection requires that each user transmit
pilot signals to its serving base station(s). The pilot signals
from different mobile units (or different antennas in each mobile
unit) can be multiplexed with the data and each other in time,
frequency, code or a combination thereof. Typically, a set of
common pilot signals are defined and divided among the various
users. For example: in an OFDMA (orthogonal frequency division
multiple access) system such as the one in FIG. 1, the tones are
divided into data tones (open circles in FIG. 1) and common pilot
tones (shaded circles in FIG. 1). Each user utilizes some of the
common pilot tones, preferably those in the vicinity of its
assigned data tones, to send its pilot signals. For example, user A
transmits on data tones at the left side of FIG. 1 and therefore
also uses the common pilots in this region. User B transmits on
data tones at the right side of FIG. 1 and therefore also uses the
common pilots in this region.
[0007] A growing trend in wireless systems is to equip receivers
with multiple antennas. Transmissions from these users are resolved
and detected by virtue of their distinct spatial characteristics
across the various receive antennas (so-called spatial multiple
access or virtual MIMO). This enables several users to share each
time/frequency/code resource, e.g., it allows multiple users to
transmit concurrently on the same frequency band and with the same
code. Detecting concurrent signals is contingent on the receiver
having estimates of the amplitude and phase of each of the user
channels. Conventional techniques for acquiring these estimates use
separate pilot transmissions from each of the users involved. The
separate pilot transmissions are used to define the user channels
corresponding to the multiple receive antennas. However, the pilot
transmissions used to define spatial channels are not
conventionally transmitted using common pilot signals because
collisions between multiple users significantly reduces the ability
of the receiver to detect the pilot signals of the separate users
and determine the amplitude and phase of the user channels.
[0008] Wireless communication systems that implement spatially
defined channels typically include dedicated pilots in addition to
the common pilots. The dedicated pilot channels can be assigned to
individual users so that the pilot signals transmitted on the
dedicated pilot channels do not collide with signals transmitted by
other users. For example: in an OFDMA (orthogonal frequency
division multiple access) system such as the one in FIG. 2, the
tones are divided into data tones (open circles in FIG. 2), common
pilot tones (shaded circles in FIG. 2), and dedicated pilot tones
(circles with shaded boundaries in FIG. 2). One range of tones on
the left-hand side of FIG. 2 is assigned to Users A and C and
another range of tones on the right-hand side of FIG. 2 is assigned
to Users B and D. Each range of tones includes data tones, common
pilot tones, and the dedicated pilot tones that can be assigned to
particular users.
[0009] Allocating some of the tones to be dedicated pilot tones has
a number of drawbacks. For example, the number of dedicated pilots
needed to support the users in the system scales with the number of
users that are performing spatial multiple access. In contrast, the
number of common pilots does not scale with the number of users
because all of the users can use the common pilot tones.
Consequently, fewer dedicated pilot tones (relative to the
potential number of common pilot tones) are typically available to
each user in a system that implements dedicated pilot tones. For
example, in FIG. 2, each user is allocated a single dedicated pilot
tone whereas in the corresponding scenario without spatial multiple
access, such as depicted in FIG. 1, each user can be allocated 2-3
common pilots. Moreover, when spatial multiple access with
dedicated pilots is implemented, the common pilots are not
typically used for channel estimation because of the high
probability of collisions between pilot signals transmitted by
different users. The common pilots may therefore represent wasted
resources. Moreover, because of the reduced number of dedicated
pilot channels and the unavailability of the common pilot channels,
spatial multiple access systems are at a disadvantage (relative to
common pilot channel systems) in terms of channel estimation
because less information may be available to estimate the spatial
channels.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to addressing the effects
of one or more of the problems set forth above. The following
presents a simplified summary of the invention in order to provide
a basic understanding of some aspects of the invention. This
summary is not an exhaustive overview of the invention. It is not
intended to identify key or critical elements of the invention or
to delineate the scope of the invention. Its sole purpose is to
present some concepts in a simplified form as a prelude to the more
detailed description that is discussed later.
[0011] In one embodiment of the present invention, a method is
provided for channel estimation implemented in a receiver having
multiple antennas configured to receive at least one common pilot
available to a plurality of users and a plurality of dedicated
pilots. Each dedicated pilot is allocated to one of the plurality
of users. The method includes estimating at least one first channel
associated with a first user and at least one second channel
associated with a second user based on observations of the
plurality of dedicated pilots and of said at least one common
pilot.
[0012] In another embodiment of the present invention, a method is
provided for channel estimation implemented in a receiver having
multiple receive antennas configured to receive at least one common
pilot available to a plurality of transmit antennas associated with
at least one user and a plurality of dedicated pilots. Each
dedicated pilot is allocated to one of the plurality of transmit
antennas. The method includes estimating a plurality of channels
associated with the plurality of transmit antennas based on
observations of the plurality of dedicated pilots and of said at
least one common pilot.
[0013] In yet another embodiment of the present invention, a method
is provided for channel estimation implemented in a plurality of
receivers each having at least one receive antenna configured to
receive at least one common pilot available to a plurality of users
and a plurality of dedicated pilots. Each dedicated pilot is
allocated to one of the users. The method includes estimating a
plurality of channels associated with the plurality of users based
on observations of the plurality of dedicated pilots and of said at
least one common pilot.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0015] FIG. 1 conceptually illustrates a first exemplary embodiment
of a conventional allocation of tones;
[0016] FIG. 2 conceptually illustrates a second exemplary
embodiment of a conventional allocation of tones;
[0017] FIG. 3 conceptually illustrates one exemplary embodiment of
the wireless communication system, in accordance with the present
invention;
[0018] FIG. 4 conceptually illustrates one exemplary embodiment of
an allocation of tones, in accordance with the present
invention;
[0019] FIG. 5 conceptually illustrates a first exemplary embodiment
of channel estimation logic, in accordance with the present
invention;
[0020] FIG. 6 conceptually illustrates a second exemplary
embodiment of channel estimation logic, in accordance with the
present invention; and
[0021] FIG. 7 conceptually illustrates a third exemplary embodiment
of channel estimation logic, in accordance with the present
invention.
[0022] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the scope of the invention as defined
by the appended claims.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0023] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions should be
made to achieve the developers' specific goals, such as compliance
with system-related and business-related constraints, which will
vary from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0024] The present invention will now be described with reference
to the attached figures. Various structures, systems and devices
are schematically depicted in the drawings for purposes of
explanation only and so as to not obscure the present invention
with details that are well known to those skilled in the art.
Nevertheless, the attached drawings are included to describe and
explain illustrative examples of the present invention. The words
and phrases used herein should be understood and interpreted to
have a meaning consistent with the understanding of those words and
phrases by those skilled in the relevant art. No special definition
of a term or phrase, i.e., a definition that is different from the
ordinary and customary meaning as understood by those skilled in
the art, is intended to be implied by consistent usage of the term
or phrase herein. To the extent that a term or phrase is intended
to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be
expressly set forth in the specification in a definitional manner
that directly and unequivocally provides the special definition for
the term or phrase.
[0025] FIG. 3 conceptually illustrates one exemplary embodiment of
a wireless communication system 300. In the illustrated embodiment,
the wireless communication system 300 includes one or more base
stations 305 (or access networks) that are used to provide wireless
connectivity to mobile units 310 over corresponding air interfaces
315. Persons of ordinary skill in the art having benefit of the
present disclosure should appreciate that other terms, such as
users, access terminals, subscriber stations, subscriber terminals,
and the like may also be used to indicate the mobile units 310.
Persons of ordinary skill in the art having benefit of the present
disclosure should also appreciate that the number of base stations
305 and/or mobile units 310 shown in FIG. 3 is intended to be
illustrative and not to limit the present invention. In alternative
embodiments, any number of base stations 305 and/or mobile units
310 may be included in the wireless communication system 300.
[0026] Wireless connectivity may be provided according to the
standards and/or protocols defined for next (4th) generation
wireless systems such as 802.16e WiMAX, UMTS Long Term Evolution
(LTE) and cdma2000 EV-DO Revision C Ultra Mobile Broadband (UMB),
which are based on Orthogonal Frequency Division Multiple Access
(OFDMA) techniques that may implement Hybrid Automatic Repeat
reQuest (HARQ) to increase the capacity of the OFDMA system.
Techniques for implementing and/or operating systems that provide
wireless connectivity according to next generation wireless
standards and/or protocols are known in the art and in the interest
of clarity only those aspects of implementing and/or operating the
systems that are relevant to the present invention will be
discussed herein. Furthermore, persons of ordinary skill in the art
having benefit of the present disclosure should appreciate that the
present invention is not limited to next generation wireless
communication systems and/or systems that implement OFDMA. In
alternative embodiments, the wireless communication system 300 may
be any generation system that operates according to other standards
and/or protocols.
[0027] The base station 305 and/or the mobile units 310 may be
equipped with multiple antennas. In the illustrated embodiment, the
base station 305 includes multiple antennas 320 that can be used to
transmit and/or receive information over the air interfaces 315.
Although only a single antenna is shown attached to each mobile
unit 310, in general the mobile units 310 may include multiple
antennas. The number of antennas 320 included in the base station
305 and/or mobile units 310 is a matter of design choice and may be
different in different embodiments of the wireless communication
system 300.
[0028] The use of multiple antennas 320 at the base station 305
allows the channels of the air interfaces 315 to be defined in
terms of the spatial characteristics of the signals transmitted
between the antennas 320 and the mobile units 310. For example, the
channel coefficients between each transmit antenna and each receive
antenna at user k can be represented as a matrix H. The
relationship between transmit and receive signals can be
represented as:
y=Hx+n
where x is a vector containing the transmit signals, y is a vector
of received signals at each antenna and n is an noise vector The
spatially defined channels may enable several users 310 to share
each time/frequency/code resource associated with the air
interfaces 315. For example, multiple mobile units 310 may be able
to transmit concurrently on the same frequency band and with the
same code. In order to detect the concurrent signals, channel
estimation logic 325 in the base station is used to make estimates
of the amplitude and phase of each of the user channels. Persons of
ordinary skill in the art having benefit of the present disclosure
should appreciate that the channel estimation logic 325 may be
implemented in hardware, firmware, software, or any combination
thereof.
[0029] In the illustrated embodiment, the channel estimation logic
325 estimates channels of the air interfaces 315 using observations
of one or more common pilots and dedicated pilots allocated to the
mobile units 310. As used herein, the phrase "common pilot" will be
understood to refer to an air interface resource (such as a time
slot, a frequency, and/or a code) that is shared by the mobile
units 310 and is used to transmit pilot signals over the air
interface 315. The phrase "dedicated pilot" will be understood to
refer to an air interface resource (such as a time slot, a
frequency, and/or a code) that is allocated to a single mobile unit
310 so that this mobile unit can transmit a pilot signal over the
air interface 315. Other mobile units 310 are excluded from using
the dedicated pilot when it has been allocated. Persons of ordinary
skill in the art having benefit of the present disclosure should
appreciate that other terms may also be used to indicate common
pilots and/or dedicated pilots. For example, in WiMAX, common
pilots are called "slot pilots" and the dedicated pilots are called
"sounding symbols."
[0030] FIG. 4 conceptually illustrates one exemplary embodiment 400
of an allocation of tones. In the illustrated embodiment, the
frequency tones are defined for an OFDMA (orthogonal frequency
division multiple access) system. Although FIG. 4 depicts the
various channels (e.g., data channels and/or pilot channels) as
being a one-dimensional distribution in frequency, persons of
ordinary skill in the art having benefit of the present disclosure
should appreciate that the present invention is not limited to this
distribution. In alternative embodiments, the channels may be
distributed in multiple dimensions corresponding to multiple
resources of the air interface. For example, the channels may
alternatively be distributed in time and frequency, e.g., the
channels may be assigned to points in a 2-dimensional
time-frequency grid or rectangle and different parts of this grid
may be allocated to data, common pilots, and dedicated pilots.
[0031] In the illustrated embodiment, the tones are allocated to
data tones (open circles in FIG. 4), common pilot tones (shaded
circles in FIG. 4), and dedicated pilot tones (circles with shaded
boundaries in FIG. 4). Each user is assigned to a portion of the
tones. In the illustrated embodiment, users A and C are assigned to
tones on the left-hand side of FIG. 4 and the users B and D are
assigned to tones on the right-hand side of FIG. 4. The users may
utilize any of the common pilot tones, preferably those in the
vicinity of its assigned data tones, to send its pilot signals. For
example, users A and C transmit on the common pilots in the
frequency band that corresponds to the tones assigned to these
users, as indicated by the label "AC" in these tones. Users B and D
transmit on the common pilots in the frequency band that
corresponds to the tones assigned to these users, as indicated by
the label "BD" in these tones.
[0032] In the illustrated embodiment, each user is also assigned
one dedicated pilot tone, as indicated by the labels "A," "B," "C,"
and "D" and the various dedicated pilot tones. Although FIG. 4
depicts the dedicated pilots as being frequencies that are assigned
to a single user for an undefined period of time, the present
invention is not limited to this allocation technique. In
alternative embodiments, users may be dynamically assigned to one
or more dedicated pilots. For example, user A may be assigned to
one dedicated pilot for a selected period of time (and/or selected
number of time slots) and then other users may be assigned to this
dedicated pilot during other periods of time (or during other time
slots). The users may also be assigned to different dedicated pilot
tones during different time periods or time slots. Furthermore,
users are not limited to using a single dedicated pilot at a time.
In some embodiments, one or more users may be assigned to more than
one dedicated pilot during a particular time period.
[0033] FIG. 5 conceptually illustrates a first exemplary embodiment
of channel estimation logic 500. In the first exemplary embodiment,
the channel estimation logic 500 estimates the channels associated
with users A and B in a two-stage channel estimation process. The
channel estimation logic 500 therefore includes channel estimators
505 that are used to form a preliminary estimate of the channels
associated with the users A and B based on the observations of the
dedicated pilots associated with these users. The channel
estimation logic 500 also includes a channel estimator 510 that is
used to estimate a superposition of the channels associated with
the users A and B based upon the observations of the common pilots
that are used by these users. The channel estimation algorithms
implemented in the channel estimators 505, 510 are matters of
design choice. However, in one embodiment, the channel estimators
505, 510 may implement a minimum mean square criterion that
estimates one or more unknowns (i.e., the channels) based upon the
available known information (i.e., the observations of the
dedicated pilots and/or common pilots). Techniques for estimating
wireless communication channels using minimum mean squared criteria
are known in the art and in the interest of clarity only those
aspects of channel estimation that are relevant to the present
invention will be discussed further herein.
[0034] The preliminary estimates of the channels associated with
the users may then be provided to estimation improvement logic 515.
The channel estimator 510 may also provide a signal that indicates
the estimate of the superposition of the channels associated with
the users A and B to the estimation improvement logic 515, which
may generate refined and/or improved estimates of the channels
associated with these users using the preliminary estimates and the
estimate of the channel superposition. In one embodiment, the
estimation improvement logic 515 uses a minimum mean square
criterion to determine the improved estimate of the channels
associated with the users A and B. The first exemplary embodiment
of the channel estimation logic 500 may be relatively simple to
implement but may provide a less accurate estimate of the channels
because the dedicated pilot information and the common pilot
information is incorporated in different stages of the problem
solution.
[0035] FIG. 6 conceptually illustrates a second exemplary
embodiment of channel estimation logic 600. In the second exemplary
embodiment, the channel estimation logic 600 includes two channel
estimators 605, 610 (i.e., one for each user) that are used to
estimate the channels for the users A and B based on observations
of the corresponding dedicated pilots and the observations of the
common pilots. For example, the channel estimator 605 receive
signals indicating the observations of the dedicated pilots
allocated to the user A and signals indicating the observations of
the common pilots that are used by both the users A and B. The
channel estimator 605 may then estimate the channels for the user A
based on the corresponding dedicated pilot and the common pilot
information. For example, the observations of the dedicated pilot
allocated to user A and the observations of the common pilots may
be used as inputs to a minimum mean square criterion algorithm,
which generates estimates of the channels for user A. The channel
estimator 610 may similarly estimate the channels for user B based
on the observations of the dedicated pilot allocated to user B and
the observations of the common pilots.
[0036] FIG. 7 conceptually illustrates a third exemplary embodiment
of channel estimation logic 700. In the third exemplary embodiment,
the channel estimation logic 700 includes one channel estimator 705
that is used to concurrently estimate the channels for the users A
and B based on observations of the corresponding dedicated pilots
and the observations of the common pilots. For example, the channel
estimator 705 may receive signals indicating the observations of
the dedicated pilots allocated to the user A, observations of the
dedicated pilot allocated to user B, and signals indicating the
observations of the common pilots that are used by both the users A
and B. The channel estimator 705 may then estimate the channels for
the user A and user B based on the corresponding dedicated pilots
and the common pilot information. For example, the observations of
the dedicated pilot allocated to user A, the observations of the
dedicated pilot allocated to user B, and the observations of the
common pilots may be used as inputs to a minimum mean square
criterion algorithm, which generates estimates of the channels for
user A and user B. Persons of ordinary skill in the art having
benefit of the present disclosure should appreciate that the
present invention is not limited to estimating channels for two
users. In alternative embodiments, the channel estimation logic 700
may estimate channels for any number of users. Although the third
exemplary embodiment of the channel estimation logic 700 may be
relatively complex to implement, e.g., compared to the first
exemplary embodiment shown in FIG. 5, the channel estimates may be
relatively more accurate because the channel estimation logic 710
can account for coupling between the observations of the dedicated
pilots and the common pilots.
[0037] The various embodiments depicted herein have assumed a
wireless communication system in which a base station equipped with
multiple antennas receives signals from multiple users concurrently
on the same frequency band and with the same code. However, persons
of ordinary skill in the art having benefit of the present
disclosure should appreciate that the present invention is not
limited to this configuration of the wireless communication system.
In alternative embodiments, the techniques described herein may be
applied in other configurations of the wireless communication
system. For example, the spatial channel estimation techniques
described herein may be applied to a single user with multiple
antennas transmitting signals simultaneously on the same frequency
band and with the same code. In this case, each antenna plays the
role of a user in the setting described herein so that dedicated
pilots are allocated to the separate antennas and used to estimate
channels associated with each antenna. For another example, the
spatial channel estimation techniques described herein may be
applied to a plurality of users, each with multiple antennas that
transmit concurrently on the same frequency band and with the same
code. Each antenna of each user plays the role of a user in the
setting described herein so that dedicated pilots are allocated to
the separate antennas and used to estimate channels associated with
each antenna. For yet another example, the spatial channel
estimation techniques described herein may be applied to a wireless
communication system that includes multiple base stations that
perform coordinated reception of pilots from one or more users.
Each of the multiple base stations may include one or more antennas
so that when the base stations are coordinated may act as a single
entity that receives communication over multiple antennas.
[0038] Portions of the present invention and corresponding detailed
description are presented in terms of software, or algorithms and
symbolic representations of operations on data bits within a
computer memory. These descriptions and representations are the
ones by which those of ordinary skill in the art effectively convey
the substance of their work to others of ordinary skill in the art.
An algorithm, as the term is used here, and as it is used
generally, is conceived to be a self-consistent sequence of steps
leading to a desired result. The steps are those requiring physical
manipulations of physical quantities. Usually, though not
necessarily, these quantities take the form of optical, electrical,
or magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
[0039] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise, or as is apparent
from the discussion, terms such as "processing" or "computing" or
"calculating" or "determining" or "displaying" or the like, refer
to the action and processes of a computer system, or similar
electronic computing device, that manipulates and transforms data
represented as physical, electronic quantities within the computer
system's registers and memories into other data similarly
represented as physical quantities within the computer system
memories or registers or other such information storage,
transmission or display devices.
[0040] Note also that the software implemented aspects of the
invention are typically encoded on some form of program storage
medium or implemented over some type of transmission medium. The
program storage medium may be magnetic (e.g., a floppy disk or a
hard drive) or optical (e.g., a compact disk read only memory, or
"CD ROM"), and may be read only or random access. Similarly, the
transmission medium may be twisted wire pairs, coaxial cable,
optical fiber, or some other suitable transmission medium known to
the art. The invention is not limited by these aspects of any given
implementation.
[0041] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within
the scope of the invention. Accordingly, the protection sought
herein is as set forth in the claims below.
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